1. Field of the Invention
The present invention relates generally to image processing apparatuses and image processing methods, and more particularly to an image processing apparatus and an image processing method that embed information in or extract information from an image.
2. Description of the Related Art
Recent improvement of image processing techniques and image forming techniques has made it possible to make such faithful copies of bills or securities (valuable papers), using a digital color copier, that the copies are not easily distinguishable from their original genuine articles. Therefore, it is necessary to take measures so that special materials such as bills and securities cannot be copied at all or correctly.
Further, for example, in company offices, general materials (documents) other than special materials such as bills and securities also include many confidential documents of which outputting such as copying is prohibited in terms of confidentiality of their contents. It is also necessary to take measures so that such confidential documents cannot be copied at all or correctly.
Therefore, conventionally, various inventions have been made to restrain special materials or confidential documents from being copied. For example, Japanese Laid-Open Patent Application No. 2004-274092 proposes the technique of preventing an image from being output if a predetermined dot pattern is detected from the image when the image is read with a scanner. Accordingly, it is possible to effectively prevent reproduction of a confidential document of which copying is prohibited by embedding the predetermined dot pattern in the confidential document in advance.
However, according to the technique disclosed in Japanese Laid-Open Patent Application No. 2004-274092, although it is possible to effectively prevent copying of a confidential document, it is only whether the document is confidential, that is, only one bit's worth of information that can be embedded in the document. In this case, if it were possible to embed more information, it would be possible to perform more flexible security control. For example, it is possible to provide such an application that determines whether to authorize or prohibit copying in accordance with the title (position) of a user in combination with user authentication.
However, now that confidential documents with printed background dot patterns in which copy control information to simply determine whether to authorize or prohibit copying with one bit's worth of information is embedded are common and copiers that perform copy prohibition control by detecting the copy control information are widely used, it is desirable that another several bits' worth of information be embeddable and compatible with the existing background dot patterns. That is, at least one-bit information should be detectable both in the case of reading a confidential original in which several-bit information is further embedded in addition to the one-bit information, using a conventional detector that can detect only one-bit information, and in the case of reading a conventional confidential document in which only the one-bit information is embedded, using a detector that can detect several bits.